How to check for a running process with Ruby?

Question

I use a scheduler (Rufus scheduler) to launch a process called "ar_sendmail" (from ARmailer), every minute.

The process should NOT be launched when there is already such a process running in order not to eat up memory.

How do I check to see if this process is already running? What goes after the unless below?

scheduler = Rufus::Scheduler.start_new

  scheduler.every '1m' do

    unless #[what goes here?]
      fork { exec "ar_sendmail -o" }
      Process.wait
    end

  end

end

Answer 1

unless `ps aux | grep ar_sendmai[l]` != ""

Answer 2

This looks neater I think, and uses built-in Ruby module. Send a 0 kill signal (i.e. don't kill):

  # Check if a process is running
  def running?(pid)
    Process.kill(0, pid)
    true
  rescue Errno::ESRCH
    false
  rescue Errno::EPERM
    true
  end

Slightly amended from Quick dev tips You might not want to rescue EPERM, meaning "it's running, but you're not allowed to kill it".